Me thinks HWlabs bit off a little more than they could chew!
HWlabs Open Letter to Koolance
Koolance's Response to Hardware Labs (June 15, 2007)
Koolance's Response to Hardware LabsThe Copper Radiator Myth
"Copper Core" radiators are touted as offering the highest performance for liquid cooling systems. Since copper has a thermal conductivity 1.8 times greater than aluminum, a copper radiator should outperform aluminum, right? Actually, this is false.
By itself, copper does indeed transfer heat more quickly than aluminum. This is why most liquid cooling companies, including Koolance, base water blocks in pure copper. But one physical property of a material does not dictate performance under every application. This is particularly evident when dealing with extremely thin materials, such as radiator walls.
Thin strips of copper can not be welded or brazed without melting. That means a louver fin radiator that claims to be "all copper" or "copper core" actually consist of multiple materials You would expect a "copper core" radiator to directly pass heat from liquid into copper. However, this radiators does not. To get a better idea of what's going on, you need to split the radiator open. (Don't worry, we'll do this for you)
Here we find this radiator to be predominantly brass. Liquid never comes into contact with pure copper, which is only used in the air fins. Therefore, this technique requires a third material to join the two metals, which means the heat transfer efficiency is significantly reduced.
Furthermore, typical brass has a thermal conductivity of about 159W/mK (37/15 Cu/Zn). Koolance uses nearly pure aluminum in its radiator fins and tubes, which has a thermal conductivity of about 237W/mK (33% greater).
Based on these points, it should not be difficult to realize that an all aluminum heat exchanger will actually transfer heat more quickly than a mixture of different materials
In extensive testing, Koolance has found our all-aluminum brazed radiators transfer heat 39-49% more efficiently than a typical claimed "copper core" radiator (per cubic centimeter of radiator).
So why would any company utilize this brass/copper radiator design? The simple reason is cost; this manufacturing technique is cheaper. Brazing a full aluminum heat exchanger requires a relatively large amount of initial expense. (See notes on corrosion.)
Similar to abandoning cheaper tube and fin copper radiators, the automotive industry long ago transitioned to all-aluminum brazed radiators for their higher level of performance.
Testing Console at KATECH
Koolance created a stir last month when we posted that HWLabs Black Ice® radiators utilized a lower-performing design to our own. It was not our original intention to point out specific radiator manufacturers. In fact, the Copper Radiator Myths page did not list any company brands or names until later, when customers requested this information. To preface this page, Koolance has found nothing wrong with the quality of HWLabs radiators.
However, after submitting samples to an independent laboratory (KATECH), we are maintaining our original argument. We also included a ThermoChill radiator during this lab analysis. The Koolance brazed full-aluminum radiator outperformed both tested brass/copper radiators relative to size. Full test results have been posted here.
Copper conducts heat more quickly than aluminum, and Koolance has never asserted otherwise. Some individuals have made the argument that this alone means a copper radiator will outperform aluminum, but that reasoning disregards the fabrication of those materials. A hypothetical heat exchanger incorporating carbon nanotubes would not necessary perform better than aluminum or copper simply because of its composition. The design matters equally!
Since HWLab's reponse, some have accused Koolance of spreading disinformation, or wrongfully questioning the "industry standard". Notwithstanding the fact we feel we're correct, where would technology be if no individuals or companies were willing to question standards? Koolance has posted this information because we felt it beneficial to discuss given the opposing viewpoint (which we feel is a general misconception).
To address HWLab's "Erroneous" assertion points:
1. "Glue is used to bind the fins to the tubes..." Koolance originally used the term "glue" improperly due to a language mistranslation. This was intended to indicate the effect of the bonding material, and not the actual material itself since various substances and techniques can be used by different companies. Our original point that a third material is used to bond copper fins to brass tubes still stands-- whether it be solder, metal powder in an adhesive, or another technique.
2. "Brass tubes in copper radiators make for poor performance..." Both radiator designs are valid, we simply stated that brazed aluminum performs better relative to size.
HWLabs here failed to comment on the thermal performance of brass, which is the only radiator material in contact with water. Typical brass has a thermal conductivity 33% lower than aluminum. So taking only relative thermal conductivities into consideration, copper is about 70% faster than aluminum, and aluminum is about 50% faster than brass. HWLabs also mentions materials thickness, and herein emphasizes our very point: these metals are less critical when such thin pieces are used.
Considering these aspects, Koolance's argument for higher performance with a 100% aluminum radiator over a brass/copper amalgamation should appear feasible.
3. "Copper is prone to oxidation and re tards performance..." Copper and aluminum both oxidize (as Cu2O and Al2O3, respectively), and each can help protect from corrosion. How significantly this affects performance is subject to debate. However, HWLab's assertion that oxidized copper is "not as dangerous" as a pinhole cavity in aluminum appears incongruous. [In an unrelated note, aluminum better protects some metals like brass from corrosion when alloyed in small amounts.]
The dissected Black Ice® heat exchanger (WT-Xtreme-BK) was not the identical one tested (WT-GTS240). It was actually purchased new from a U.S. reseller, and water was never run through it. Therefore, contrary to HWLab's implication, Koolance did not "accelerate" oxidation, and we would have to assume someone who dissected that particular model of radiator would encounter similar results. It is certainly possible the unit was used before we purchased it, or else attributable to a manufacturing anomaly.
4. "Aluminum is always the best..." What Koolance maintains, is that an all-aluminum brazed heat exchanger of identical size as a brass/copper heat exchanger will have a higher heat dissipation potential. The lab's results demonstrate this.
The required initial investment in manufacturing equipment is normally greater for aluminum heat exchangers than brass/copper. Naturally, the per unit cost for either radiator design can be reduced with sufficient production.
HWLabs indicated that [copper] round tube and fins have not been used in automobiles for over 50 years. Koolance did not describe the tube and fin heat radiator in detail on the myths page. We linked to a separate page describing the disadvantages of this design because some PC cooling companies still utilize this technology. It is not strictly relevant to Koolance's base argument for aluminum versus brass/copper louver fin style heat exchangers.
Koolance is not bound by any particular heat exchanger technique. If we decided that aluminum's advantages no longer outweighed an alternative, we would change for the benefit of our customers! We are already in the process of increasing the thickness and flow rate of our heat exchangers to further their performance over brass/copper.
Heat Exchanger Lab Results
Heat Exchanger Lab Results (Continued)
The Copper Radiator Myth